Highly discriminating distance-based topological index

A new topological indexJ (based on distance sumss_i as graph invariants) is proposed. For unsaturated or aromatic compounds, fractional bond orders are used in calculatings_i. The degeneracy ofJ is lowest among all single topological indices described so far. The asymptotic behaviour ofJ is discussed, e.g. whenn → ∞ in C_nH_{2n = 2},Jar π for linear alkanes, andJ → ∞ for highly branched ones.     

A kinetic study of the infrared multiphoton dissociation of s-trioxane

The IR multiple photon dissociation of s-trioxane is reported. The molecule is dissociated with high efficiency at low fluences (i.e. 6 J cm^?2) At high s-trioxane pressures, the dissociation is enhanced via V-V processes. Addition of He results in V-T deactivation of the energized molecule. The dissociation is well described by RRKM theory.     

Large-scale MCHF calculations of hyperfine structures in nitrogen and oxygen

The hyperfine structure constants for the 1s ²2s ²2p ³ -⁴ S ^o ground state in nitrogen and the 1s ²2s ²2p ³3s ⁵ S ^o excited state in oxygen are calculated using the MCHF Atomic Structure Package. The single excitation picture is explored through the use of compact wave functions allowing radial non-orthogonalities. Electron correlation is described through numerical multiconfiguration Hartree-Fock calculations for configuration expansions obtained by allowing all single and double excitations from the reference configuration to an active set of orbitals. The latter is increased in a systematic way allowing the convergence of the hyperfine parameters to be studied. Three- and four-particle effects are shown to be important and are taken into account in a sequence of large configuration interaction calculations. The final results are in good agreement with experiment.     

Cyanoamino compounds in synthesis syntheses of some heterocycles

Transformations of some heterocyclic cyanoamino compounds leading to various heterocyclic systems are described.s-Triazolo (1,5-α)azines are obtained either in a direct synthetic approach or via the substituted aminotetrazoles, substituted 3-amino-5-oxo-1,2,4-oxadiazolines, and fromN-ethoxycarbonylN′-heteroaryl thioureas orN-heteroarylN′-hydroxyguanidine. The cyanoamino group reacts also witho-difunctional benzenes to give the corresponding substituted derivatives of benzimidazole, benzoxazole or benzothiazole.     

Linewidth dependence of quasi-stationary states in large molecules

We study the quasi-stationary states, or eigenstates, of the decay matrix for a system described by one single vibronic state |s〉 coupled to a manifold {l}, both |s〉 and {l} levels being coupled to separate continua which endow them with finite linewidths γ_s, γ_l. When all the zero-order states have the same linewidth (not necessarily zero) the quasi-stationary states are identical to the molecular eigenstates; when the difference between the linewidths γ_s ? γ_l is large enough, the zero-order sets (s, {l}) are completely decoupled, a result which has been established for the two-level system. We indicate some consequences of collisional broadening involving pressure effects in the gas phase.     

The Ar16+ 23 S 1 lifetime from a measurement on recoil ions

Slow highly-charged Ar recoil ions have been produced by heavy-ion atom collisions. A time-of-flight measurement of 3 keV x-rays in coincidence with recoil ion charge state has lead to a value of (203±12)ns for the mean life of the Ar¹⁶⁺ 1s2s ³ S ₁ state. The experimental procedure is described and compared to earlier measurements of the same entity using fast ion beams.     

Thermodynamic properties of simple alkenes

Employing low temperature thermal measurements, heat capacities (C_s) in the crystal and liquid states, and phase transition data, T_m and ΔH_m, the condensed phase thermodynamic properties, (G_s -H°₀)/T, H_s -H°₀, S_s and C_s, in the temperature range 0–360 K were evaluated for the following eleven alkenes: ethylene, propylene, 1-butene, cis-2-butene, trans-2-butene, 1-pentene, cis-2-pentene, trans-2-pentene, 2-methyl-1-butene, 3-methyl-1-butene and 2-methyl-2-butene. The sources of experimental data, methods of evaluation, and the calculated results are described in detail.     

Intra- and inter-atomic auger processes in collisions of low energy He++, He+, He* (23,S, 21 S) and Li+ with Li covered W(110) surfaces

Electron spectra from He⁺⁺, He⁺ and Li⁺ (10 to 1500 eV) ions colliding under grazing incidence with Li covered W (110) surfaces are reported. The results are compared with those obtained from thermal collisions of (2³ S; 2¹ S) metastable He atoms. In these collisions 1s vacancies are either produced during the collision event (energetic He⁺ (Li ⁺) collisions) or are brought into the collision (slow He⁺⁺ (He⁺, He*) collisions). Population of the 2s orbitals by two electrons produces states which decay by intraatomic Auger processes: we observe autoionization of He** (2s ²) and Li** (1s 2s ²) as well as autodetachment of He^?* (1s 2s ²). Alternatively the 1s-holes in the projectile or target (Li) can be filled by Auger processes involving one or two surface electrons. The processes leading to electron emission are studied as a function of the Li coverage in the submonolayer region (0≦Θ_Li≦1Ml) and as a function of the projectile energy. It is concluded that with one or two 1s vacancies present in the projectile the double capture of two surface electrons constitutes an important process responsible for electron emission of low work function surfaces.     

Multiple collisions in molecular beam scattering experiments

Due to the forward peaked differential cross section for elastic atom—atom scattering the effect of multiple collisions has to be considered in the analysis of crossed beam measurements of the total cross section and especially of the small angle differential cross section at large values of the beam attenuation. At angles θ ≈ θ₀, with θ₀ the quantum mechanical scaling angle of the elastic differential cross section, the correction for the latter case amounts to 20% at beam attenuations I/I₀ = exp(?1). Firstly, a careful analysis of the probabilities for single and multiple scattering is given, resulting in an expression for the measured beam signals which is correct for all values of the beam attenuation. The probability for multiple scattering is then calculated for an inverse power potential V(r) = ?C_sr^?s, with s = 4 through s = 7, which include both the case of ion—atom scattering (s = 4) and atom—atom scattering (s = 6). The results are given as effective differential cross sections σ_n(θ) for n-fold scattering. They are described by a single, simple analytical function with four free parameters that have been determined for n = 2, 3 and 4 by a least squares method. The σ_n(θ) are normalised to the total cross section Q.     

Fine structure of the 1s5f and 1s5g levels of He I

The fine structure of the 1s5f and 1s5g levels of He I was measured using microwave spectroscopy. The helium atoms were excited by ion impact, and the eleven allowed 1s5f ^2S+1 F _J –1s5g ^2S′+1 G _J , transitions near ν≈15 GHz were induced and detected by measuring the 1s4d–1s2p or 1s3d–1s2p spectral-line intensities of the impact radiation as a function of the microwave frequency. The measured transition frequencies are in accord with theoretical values and, except for one transition frequency, with earlier experimental data. The existing discrepancy between these earlier data and theory could be solved.     

The structure and oscillational motion of 57Fe atoms in interstitial sites in Al as determined from interference of Mössbauer γ radiation

The first excited site of the ⁵⁷Fe atom entrapped in an interstitial site in aluminum, as reported by W. Petry, G. Vogl, and W. Mansel (Phys. Rev. Lett.45, 1862 (1980)). from a Mössbauer spectroscopic study of a single crystal, is analyzed by consideration of the value of the Hooke's law constant of the FeAl bonds obtained from the values for elemental Fe and Al. The eight wavefunctions for the eightfold nearly degenerate excited state are described as 2s1p1d1f hybrids of three-dimensional harmonic oscillator wavefunctions relative to the center of the undistorted Al₆ octahedron or as localized 1s functions relative to the center of the distorted octahedron. These considerations provide a qualitative understanding of the observations on this system.     

Synthesis and electrochemical characterization of donor-acceptor phenylazomethine dendrimers

The synthesis of the first donor-acceptor phenylazomethine dendrimers (4 and 5) is described. A convergent method is used via the condensation of aromatic ketones with an appropriately functionalized tri(aminophenyl)-s-triazine promoted by titanium (IV) chloride. Cyclic voltammetry investigations show a donor-acceptor behaviour due to the presence of the electron acceptor s-triazine core and the donor ability of the conjugated peripheral butoxybenzene units.     

Difference in the Tunnel Current–Tunnel Gap Width Dependence of Molecule–Adsorbed and Non–Adsorbed Graphite Measured by Means of Tunnel Gap Imaging

The tunnel gap imaging (TGI) technique is used to measure local tunnel current (I) to tunnel gap width (s) dependences (the I–s characteristics) of molecule–adsorbed and non–adsorbed surface of highly orientated pyrolytic graphite under atmosphere. When the bias voltage of several hundreds of millivolts were applied to the sample, the I–s characteristics of molecule–adsorbed sample exhibited clear bending while those of non–adsorbed sample did not. The I–s characteristics at small s region were found to be similar to those of non–adsorbed sample, but those at large s regions were absolutely different. Barrier heights calculated from the I–s characteristics at large s region for the molecule–adsorbed sample were found to be 2 or 3 orders lower than those at small s region were. The tunnel current dominant at large s region was estimated to be the inelastic tunnel current by its bias voltage dependence. The mechanism of molecular image formation in STM is discussed based on the presence of the inelastic tunnel current.     

Kinetic study of isothermal oil shale pyrolysis: 1. Mathematical model of the evolution of organic pyroproducts

An isothermal fluidized bed reactor was used for a kinetic study of oil shale pyrolysis. The rate of volatile hydrocarbon evolution was monitored by flame ionization detector. An innovative approach to the data obtained, which we adopted in the present study, led us to a simple kinetic model. The rate of volatile hydrocarbon evolution is described as a linear combination of three parallel independent first-order reactions characterized by three rate constants, k₁ = 2.6·10⁶ exp(−23.6 kcal/RT) s⁻¹, k₂ = 2.3·10⁶ exp(−26.0 kcal/RT) s⁻¹ and k₃ = 9.3·10⁵ exp(−28.1 kcal/RT) s⁻¹. The kinetic effect due to the particle size of the sample is probably due to heat transfer effects.     

Highly diastereoselective conjugate additions of monoorganocopper reagents to chiral imides

Stereoselective conjugate additions to chiral N-enoyl amides employing various monoorganocuprate reagents, Li[RCuI], are described. The presence of TMSI in the addition of Li[RCuI] in THF provided the highest stereoselectivities. Reversed major diastereomeric ratios were obtained employing Li[RCuI] in ether or conventional copper-promoted Grignard reagents. The results presented support the favored anti-s-cis conformation of the substrates using Li[RCuI]/TMSI in THF, while the copper-promoted Grignard reagents or the Li[RCuI] reagents in ether favor the opposite syn-s-cis conformation. Influence of lithium ions on the stereoselective conjugate addition of the monoorganocuprate reagent, Li[BuCuI], has been investigated and two different mechanistic pathways are presented. The results show that iodotrimethylsilane (TMSI) is crucial for the asymmetric conjugate addition of the copper reagent, but only in THF or when 12-crown-4 is used. The reaction is thought not to involve any halosilane in any critical steps in the organocopper mechanisms conducted in ether. The (CuI)₄(SMe₂)₃ complex precursor plays an instrumental role for the conjugate addition using monoorganocopper reagents.     

Effet sterique sur les vitesses de transfert protonique: cyclohexanols substitues dans le dimethylsulfoxyde

Steric effects on proton transfer from, and to, hydroxylic oxygen have been studied in a series of seventeen α-methyl and a-benzyl cyclohexanols in anhydrous DMSO, under both acid and base catalysed conditions, using dynamic MNR techniques. The protonation rate constants (k₁ ? 10⁶ M^-1 s^-1 at 25°C) obey a Taft-Ingold relationship, containing only a steric contribution E_s = E_s^OH + E_s^α, where: E_s^OH = 0 or 0.15 for an axial or equatorial hydroxyl respectively and E_s^α = ?0.070 (or ?0.115) for substituting an α-hydrogen by a methyl (or benzyl) group. An equatorial hydroxylic function is therefore 40% more reactive than its axial homologue. These kinetic data are fairly consistent with structural information resulting from IR spectroscopy (v_co and v_OH vibrations) and from NMR (hydroxylic chemical shifts and coupling constants).     

Synthesis of new unsymmetrical optically active (s)-(+)-naproxen dendrimers

Preparation of new unsymmetrical optically active (s)-(+)-naproxen dendrimers containing 2-hydroxymethyl-1,4-butanediol and 2,2-bis(hydroxymethyl)-1,4-butanediol cores is described. These polyarylester dendrimers are unsymmetrical with respect to chain lengths and aid in studying controlled drug delivery based on differential enzymatic cleavage. Synthesis of a new acid dendritic wedge containing (s)-(+)-naproxen is also reported.     

Circulardichroismus. XXX

A simple device is described which can be used with the Roussel-Jouan Dichrograph to give direct readings of Δs and Δε/λ, resp. Integration of the latter curve with a planimeter yields the rotatory strength of any partial CD-band.     

Preparation of 2,2-disubstituted 1,2-dihydro-3H-indol-3-ones via oxidation of 2-substituted indoles and Mannich-type reaction

A novel preparative method for 2,2-disubstituted 1,2-dihydro-3H-indol-3-ones through the oxidation of 2-arylindoles followed by a Mannich-type reaction with carbon nucleophiles is described.     

A fluoroimmunoassay for screeing of hepatitis B surface antigen

A fast, sensitive sandwich fluorimmunoassay for hepatitis B surface antigen (HB_s-ag) is described. Rabbit antibodies to HB_s-ag are covalently bound to the centre of a glass-fiber filter disk. The second antibody is a swine anti-human HB_s-ag conjugated with β-d-galactosidase from E. coli. The substrate is 4-methylumbelliferyl-β-d-galactopyrano-side. The technique is applied with the Stratus system which does the entire test in 8 min. the detection limit is 1 ng ml^?1, and the results correlate well with a radioimmunoassay technique.